Photothermal imaging as a new tool for the investigation of the temperature-dependent properties of the medium in nanoscale

Photothermal imaging is a powerful technique to detect small light-absorbing nanoparticles down to 1.4 nm with a high spatial resolution (1). The signal magnitude is proportional to the absorption cross-section of the nanoparticle as well as properties of the medium. Finite thermal diffusivity of the medium causes a phase delay in the response of the heat dissipation. The phase delay at each point integrated over the resolution disk is identified as the photothermal signal phase that depends on the material property (2). In this study, first, we demonstrate that the photothermal phase is capable of monitoring the local medium modifications, with high sensitivity. Second, we determine that, with the aid of simulation, information about the temperature-dependent properties of the medium, such as heat conductivity is attainable in nanoscale.
(1) Berciaud, S., Lasne, D., Blab, G. A., Cognet, L., & Lounis, B. (2006). Photothermal heterodyne imaging of individual metallic nanoparticles: Theory versus experiment. Physical Review B, 73(4), 045424.
(2) Heber, A., Selmke, M., & Cichos, F. (2015). Thermal diffusivity measured using a single plasmonic nanoparticle. Physical Chemistry Chemical Physics, 17(32), 20868-20872.